Wireless energy transfer for mobile device applications

ABSTRACT

A current sensing system and method for wireless energy transfer may include a printed circuit board, wherein the printed circuit board may include at least a first layer, a second layer, and a third layer. A loop of conductive material may be included, wherein the loop of conductive material may include a diameter D 3  on the second layer. A coil of conductive material may be included, wherein the coil of conductive material may have at least 2 turns, wherein a majority of the coil of conductive material may occupy the first layer and the third layer with an outer diameter D 1  and an inner diameter D 2 , connected through each of the first, second, and third layers. The loop of conductive material may be coupled to the coil of conductive material.

RELATED CASES

This application claims the benefit of U.S. Provisional Application No.61/980,420 filed on 16 Apr. 2014, U.S. Provisional Application No.61/981,983 filed on 21 Apr. 2014, U.S. Provisional Application No.62/024,419 filed on 14 Jul. 2014, U.S. Provisional Application No.62/059,035 filed on 2 Oct. 2014, U.S. Provisional Application No.62/078,379 filed on 11 Nov. 2014, and U.S. Provisional Application No.62/079,817 filed on 14 Nov. 2014, the contents of which are allincorporated by reference.

BACKGROUND

Energy or power may be transferred wirelessly using a variety of knowntechniques for, e.g., the purpose of doing work, such as for powering orcharging electrical devices. For example, wireless power transfersystems (e.g., highly resonant wireless power transfer systems) mayinclude high quality factor resonators that may be driven to generateoscillating electromagnetic fields and that may interact withoscillating magnetic fields to generate currents and/or voltages inelectronic circuits. That is, energy may be transferred wirelessly usingoscillating magnetic fields. For instance, wireless energy exchangebetween a source resonator (e.g., coupled to a power supply such as ACmains, battery, solar panels, etc.) and a remote resonator (e.g.,integrated with electronic mobile devices, enclosures, sleeves, cases,covers, chargers, etc.) may exchange wireless energy, which as notedabove, may be used to power or charge the associated electronic mobiledevice.

The wireless energy exchange between the source resonator and the remote(device) resonator may be optimized when the resonators are tuned tosubstantially the same frequency and when the losses in the system areminimal. As a non-limiting example, remote devices, such as a smartphone or other mobile electronic device, may be powered directly, usingthe wirelessly supplied power or energy, or the devices may be coupledto an energy storage unit such as a battery, a super-capacitor, anultra-capacitor, or the like (or other kind of power drain), where theenergy storage unit may be charged or re-charged wirelessly, and/orwhere the wireless power transfer mechanism may be supplementary to themain power source of the device. However, while known resonator designsmay be optimized while at a distance, these resonators may be lessoptimal, e.g., in closer proximity. For instance, as a non-limitingexample, the source resonator may detune the device resonator as eachresonator moves closer in proximity to one another. Additionally, knowncurrent sensing techniques that may be used for wireless energy transfermay, e.g., have excessive loss and power dissipation for the highcurrent and high frequencies used in some types of wireless energytransfer, may have frequency restrictions used in wireless energytransfer, may be susceptible to magnetic interference, may be expensive,and may add to the size of the overall devices.

BRIEF SUMMARY OF DISCLOSURE

In one example implementation, a wireless energy transfer system mayinclude but is not limited to a first layer of conductive material thatmay be positioned proximate to a second layer. The second layer ofmagnetic material may be positioned proximate to the first layer ofconductive material and a third layer. The third layer may be positionedproximate to the second layer and a fourth layer, wherein the thirdlayer may include a first resonator coil, wherein the first resonatorcoil may be configured to transfer wireless energy to a second resonatorcoil when the second resonator coil is proximate to the first resonatorcoil. The fourth layer may be positioned proximate to the third layer,wherein the fourth layer may include a plurality of conductive material.

One or more of the following example features may be included. At leastone of a size, a shape, and a geometric position of the plurality ofpieces of conductive material may reduce inductance shifting in thesecond resonator coil when the first resonator coil is proximate to thesecond resonator coil. The shape may be a rectangle. The shape may be asquare. At least a first portion of the plurality of pieces of theconductive material may be a first shape, and wherein at least a secondportion of the plurality of pieces of the conductive material may be asecond shape. At least a portion of the plurality of pieces of theconductive material may be arranged in a checkered pattern relative tothe first resonator coil. The first resonator coil may include coppertrace. For example, at least a portion of the trace may include copper.The magnetic material may include ferrite. For example, at least aportion of the magnetic material may include ferrite. The plurality ofpieces of conductive material of the fourth layer may include copper.The first layer of conductive material may include copper. The first,layer may be coupled to a surface of a mobile battery unit. The magneticmaterial may have a thickness less than 1 mm. The magnetic material mayhave a thickness less than 0.5 mm. The first resonator coil may beconfigured to transfer at least 5 W of energy to the second resonatorcoil. The first resonator coil may be configured to transfer at least 10W of energy to the second resonator coil.

In another example implementation, a wireless energy transfer system mayinclude but is not limited to a first layer of conductive material thatmay be positioned proximate to a second layer. The second layer ofmagnetic material may be positioned proximate to the first layer ofconductive material and a third layer. The third layer may be positionedproximate to the second layer and a fourth layer, wherein the thirdlayer may include a plurality of pieces of conductive material. Thefourth layer may be positioned proximate to the third layer, wherein thefourth layer may include a first resonator coil, wherein the firstresonator coil may be configured to transfer wireless energy to a secondresonator coil when the second resonator coil is proximate to the firstresonator coil.

One or more of the following example features may be included. At leastone of a size, a shape, and a geometric position of the plurality ofpieces of conductive material may reduce inductance shifting in thesecond resonator coil when the first resonator coil is proximate to thesecond resonator coil. The shape may be a rectangle. The shape may be asquare. At least a first portion of the plurality of pieces of theconductive material may be a first shape, and wherein at least a secondportion of the plurality of pieces of the conductive material may be asecond shape. At least a portion of the plurality of pieces of theconductive material may be arranged in a checkered pattern relative tothe first resonator coil. The first resonator coil may include coppertrace. The magnetic material may include ferrite. The plurality ofpieces of conductive material of the third layer may include copper. Thefirst layer of conductive material may include copper. The first layermay be coupled to a surface of a mobile battery unit. The magneticmaterial may have a thickness less than 1 mm. The magnetic material mayhave a thickness less than 0.5 mm. The first resonator coil may beconfigured to transfer at least 5 W of energy to the second resonatorcoil. The first resonator coil may be configured to transfer at least 10W of energy to the second resonator coil.

In another example implementation, a resonator for a wireless energytransfer system may include but is not limited to a first resonatorcoil, wherein the first resonator coil may be configured to transferwireless energy to a second resonator coil when the first resonator coilis proximate to the second resonator coil. A first winding of trace maybe included in the first resonator coil, wherein the first winding oftrace may include conductive material. A second winding of trace may beincluded in the first resonator coil, wherein the second winding oftrace may include conductive material. A portion of the trace of thefirst winding may cross over a portion of the trace of the secondwinding at a crossover point.

One or more of the following example features may be included. Theportion of the trace for the first winding may cross over the portion ofthe trace for the second winding at the crossover point without physicalcontact between the portion of the trace for the first winding and theportion of the trace for the second winding. The first resonator coilmay be printed on a printed circuit board, wherein the portion of thetrace for the first winding may stop on a first side of the printedcircuit board at the crossover point and may continue on a second sideof the printed circuit board, wherein the portion of the trace for thesecond winding on the second side of the printed circuit board may stopon the second side and may continue on the first side after thecrossover point. The portion of the trace for the first winding may stopon the first side of the portion of the trace for the second winding ona first layer of a printed circuit board before reaching the crossoverpoint, and may continue on the second side of the portion of the tracefor the second winding on a second layer of the printed circuit boardafter reaching the crossover point. A second portion of the trace forthe first winding may cross over a second portion of the trace for thesecond winding at a symmetrical crossover point. The crossover point mayoccur in a middle portion of the first resonator coil. The crossoverpoint may occur in an end portion of the first resonator coil. The traceof at least one of the first winding and second winding may includecopper coil. A first layer of conductive material may be included andpositioned proximate to a second layer. The second layer of magneticmaterial may be included and positioned proximate to the first layer ofconductive material and a third layer. The third layer may be includedand positioned proximate to the second layer and a fourth layer, whereinthe third layer may include a first resonator coil. The fourth layer maybe included and positioned proximate to the third layer, wherein thefourth layer may include a plurality of pieces of conductive material.

In another example implementation, a wireless energy transfer system mayinclude but is not limited to a first layer of conductive material thatmay be positioned proximate to a second layer. The second layer ofmagnetic material may be included and positioned proximate to the firstlayer of conductive material and a third layer. The third layer may bepositioned proximate to the second layer and a fourth layer, wherein thethird layer may include a first resonator coil, wherein the firstresonator coil may be configured to transfer wireless energy to a secondresonator coil when the first resonator coil is proximate to the secondresonator coil. A first winding of trace may be included in the firstresonator coil, wherein the first winding of trace may includeconductive material. A second winding of trace may be included in thefirst resonator coil, wherein the second winding of trace may includeconductive material. A portion of the trace for the first winding maycross over a portion of the trace for the second winding at a crossoverpoint. The fourth layer may include a plurality of pieces of conductivematerial.

One or more of the following example features may be included. Theportion of the trace for the first winding may cross over the portion ofthe trace for the second winding at the crossover point without physicalcontact between the portion of the trace for the first winding and theportion of the trace for the second winding. The first resonator coilmay be printed on a printed circuit board, wherein the portion of thetrace for the first winding may stop on a first side of the printedcircuit board at the crossover point and may continue on a second sideof the printed circuit board, wherein the portion of the trace for thesecond winding on the second side of the printed circuit board may stopon the second side and may continue on the first side after thecrossover point. The portion of the trace for the first winding may stopon the first side of the portion of the trace for the second winding ona first layer of a printed circuit board before reaching the crossoverpoint, and may continue on the second side of the portion of the tracefor the second winding on a second layer of the printed circuit boardafter reaching the crossover point. A second portion of the trace forthe first winding may cross over a second portion of the trace for thesecond winding at a symmetrical crossover point. The crossover point mayoccur in a middle portion of the first resonator coil. The crossoverpoint may occur in an end portion of the first resonator coil. The traceof at least one of the first winding and second winding may includecopper coil. At least one of a size, a shape, and a geometric positionof the plurality of pieces of conductive material may reduce inductanceshifting in the second resonator when the first resonator coil isproximate to the second resonator coil.

In another example implementation, a current sensing system for wirelessenergy transfer may include but is not limited to a printed circuitboard, wherein the printed circuit board may include at least a firstlayer, a second layer, and a third layer. A loop of conductive materialmay be included, wherein the loop of conductive material may include adiameter D3 on the second layer. A coil of conductive material may beincluded, wherein the coil of conductive material may have at least 2turns, wherein the coil of conductive material may occupy the firstlayer and the third layer with an outer diameter D1 and an innerdiameter D2, connected through each of the first, second, and thirdlayers. The loop of conductive material may be coupled to the coil ofconductive material.

One or more of the following example features may be included. A currentvalue of a conductor may be measured by routing the conductor throughthe inner diameter D2 of the coil of conductive material. The conductormay be part of a resonator coil. A parallel resonant circuit may beincluded and may remove harmonic content. A differential amplifier witha voltage output may be included. Peak detector circuitry may beincluded and may include an operational amplifier to track a peak of thevoltage output and determine a measured current value of a conductor. Afourth layer proximate to the second and third layers may be included,wherein the fourth layer may include an additional loop of conductivematerial coupled to at least one of the loop of conductive material andthe coil of conductive material, wherein the additional circular loop ofconductive material may have a diameter D3 on the fourth layer. The coilof conductive material may include copper trace. The coil of conductivematerial may be configured with at least one of a straight return and abalanced winding. Currents with frequencies within a range of 85 kHz to20 MHz may be configured to be measured. The coil of conductive materialmay have at least 15 turns.

In another example implementation, a method, performed by a currentsensing system, may include but is not limited to driving a conductorwith alternating current. An amplitude value and phase value of thealternating current may be measured using the current sensing system.

The details of one or more example implementations are set forth in theaccompanying drawings and the description below. Other possible examplefeatures and/or possible example advantages will become apparent fromthe description, the drawings, and the claims. Some implementations maynot have those possible example features and/or possible exampleadvantages, and such possible example features and/or possible exampleadvantages may not necessarily be required of some implementations.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example diagrammatic view of a wireless energy transfersystem according to one or more example implementations of thedisclosure;

FIG. 2A is an example diagrammatic view of a device resonator coilaccording to one or more example implementations of the disclosure andFIG. 2B is an example diagrammatic view of a source resonator coilaccording to one or more example implementations of the disclosure;

FIG. 3 is an example diagrammatic view of a device resonator accordingto one or more example implementations of the disclosure;

FIG. 4 is an example diagrammatic view of a wireless energy sourceaccording to one or more example implementations of the disclosure;

FIG. 5 is an example diagrammatic view of a wireless energy transfersystem according to one or more example implementations of thedisclosure;

FIG. 6 is an example diagrammatic view of a wireless energy sourceaccording to one or more example implementations of the disclosure;

FIG. 7 is an example diagrammatic view of a wireless energy transfersystem according to one or more example implementations of thedisclosure;

FIG. 8 is an example diagrammatic view of a wireless energy transfersystem according to one or more example implementations of thedisclosure;

FIG. 9 is an example diagrammatic view of a wireless energy sourceaccording to one or more example implementations of the disclosure;

FIG. 10 is an example diagrammatic view of a wireless energy sourceaccording to one or more example implementations of the disclosure;

FIGS. 11A-11B are example diagrammatic views of wireless energy transfersystems according to one or more example implementations of thedisclosure;

FIGS. 12A-12H are example diagrammatic views of layers of a wirelessenergy source according to one or more example implementations of thedisclosure;

FIG. 13 is an example diagrammatic view of a source resonator coilaccording to one or more example implementations of the disclosure;

FIG. 14A is an example diagrammatic view of one or more source resonatorcoils according to one or more example implementations of thedisclosure, FIGS. 14B-14C are example diagrammatic views of wirelessenergy transfer systems according to one or more example implementationsof the disclosure, and FIG. 14D is an example diagrammatic view oflayers of a source resonator coil according to one or more exampleimplementations of the disclosure;

FIG. 15 is an example diagrammatic view of a source resonator coilaccording to one or more example implementations of the disclosure;

FIG. 16 is an example diagrammatic view of a source resonator coilaccording to one or more example implementations of the disclosure;

FIG. 17 is an example diagrammatic view of a source resonator coilaccording to one or more example implementations of the disclosure;

FIG. 18 is an example diagrammatic view of a source resonator coilaccording to one or more example implementations of the disclosure;

FIGS. 19A-19B are example diagrammatic views of source resonator coilsaccording to one or more example implementations of the disclosure;

FIG. 20 is an example diagrammatic view of a source resonator coilaccording to one or more example implementations of the disclosure;

FIG. 21 is an example diagrammatic view of a current sensor for awireless energy transfer system according to one or more exampleimplementations of the disclosure;

FIG. 22 is an example diagrammatic view of a current sensor for awireless energy transfer system according to one or more exampleimplementations of the disclosure;

FIG. 23 is an example graph of output measurements of an example currentsensor for a wireless energy transfer system according to one or moreexample implementations of the disclosure;

FIG. 24 is an example schematic diagrammatic view for a current sensorfor a wireless energy source according to one or more exampleimplementations of the disclosure;

FIG. 25 is an example schematic diagrammatic view for a current sensorfor a wireless energy source according to one or more exampleimplementations of the disclosure; and

FIG. 26 is an example graph of output measurements of an example currentsensor for a wireless energy transfer system according to one or moreexample implementations of the disclosure.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Various aspects of wireless power transfer systems are disclosed, forexample, in commonly owned U.S. Patent Application Publication No.2010/0141042 A1, U.S. Patent Application Publication No. 2014/0049118A1, U.S. Patent Application Publication No. 2012/0119569 A1, and U.S.Patent Application Publication 2013/0069753 A1, the entire contents ofwhich are incorporated by reference herein.

As noted above, energy or power may be transferred wirelessly using avariety of known techniques for, e.g., the purpose of doing work, suchas for powering or charging electrical devices. For example, wirelesspower transfer systems (e.g., highly resonant wireless power transfersystems) may include high quality factor resonators that may be drivento generate oscillating electromagnetic fields and that may interactwith oscillating magnetic fields to generate currents and/or voltages inelectronic circuits. That is, energy may be transferred wirelessly usingoscillating magnetic fields. For instance, wireless energy exchangebetween a source resonator (e.g., coupled to a power supply such as ACmains, battery, solar panels, etc.) and a remote (device) resonator(e.g., integrated with mobile devices, enclosures, sleeves, cases,covers, chargers, etc.) may exchange wireless energy, which as notedabove, may be used to power or charge the associated mobile device.Resonators, such as electromagnetic resonators, may include an inductiveelement (e.g., a loop of conductive material such as copper), adistributed inductance, or a combination of inductances, withinductance, L, and a capacitive element, a distributed capacitance, or acombination of capacitances, with capacitance, C. Provided with initialenergy, such as electric field energy stored in the capacitor, thesystem may oscillate as the capacitor discharges transferring energyinto magnetic field energy stored in the inductor which in turn maytransfer energy back into electric field energy stored in the capacitor104. The terms “loop” or “coil” may be used to indicate generally aconducting structure (e.g., wire, tube, strip/trace, etc.), that mayenclose or encompass a surface of any shape and dimension, with anynumber of turns. More in-depth descriptions and examples of resonatorsfor wireless energy transfer may be found in one or more of theabove-noted commonly owned patent applications.

Referring at least to FIG. 1, an example representation of a wirelessenergy transfer system 100 is shown. In some implementations, wirelessenergy transfer system 100 may be for mobile device applications, andmay include, e.g., one or more sources (e.g., source 104) and one ormore devices (e.g., device 102). In some implementations, a power supplycoupled to a source may be a direct current (DC) (e.g., battery or otherDC power source) or an alternating current (AC) (e.g., wall source orother AC power source). In some implementations, a microcontroller(e.g., microcontroller 106) may drive a power amplifier (e.g., poweramplifier 108) at an operating frequency. In some implementations,microcontroller 106 may be used to drive power amplifier 108 as a meansof in-band communication. The resonant frequency of a source resonator(e.g., source resonator 110) may be the same as the operating frequency.In some implementations, the operating frequency may include so-called“high frequencies”, which may be equal to or greater than 85 KHz,greater than 200 KHz, or greater than 1 MHz. In some implementations,the operating frequency may include high frequencies, such as 6.78 MHzor 13.56 MHz. It will be appreciated that various other frequencies,including lesser frequencies than noted above, may be used withoutdeparting from the scope of the disclosure. In some implementations,power amplifier 108 may be, e.g., a class D or E amplifier. However, itwill be appreciated that other classes of amplifiers may be used withoutdeparting from the scope of the disclosure. Source 104 may have a meansof out-of-band wireless communication with device 102, such as Bluetoothor WiFi.

In some implementations, the wireless energy device (e.g., device 102)may include a device resonator (e.g., device resonator 112) designed tocapture oscillating magnetic fields generated by the wireless energysource (e.g., source 104 via source resonator 110). Device 102 may alsohave a means of out-of-band wireless communication with source 104.Device 102 may include a controller (e.g., embedded controller 114) tomanage power. The output of device 102 may be a load, such as a battery,appliance, mobile electronic device, etc. It will be appreciated thatvarious other aspects of device 102 and source 104, such as impedancematching networks, etc. may be included without departing from the scopeof the disclosure. More in-depth descriptions and examples of sources,devices, and their associated interactions/uses for wireless energytransfer may be found in one or more of the above-noted commonly ownedpatent applications. As such, the examples and descriptions of anyparticular implementations (e.g., configurations, components, electronicdevices) of the disclosure should be taken as examples only and not tootherwise limit the scope of the disclosure.

In some implementations, one or more device resonators and theirassociated electronics may be integrated into an enclosure of a mobiledevice. For example, as will be discussed in greater detail below, theresonator and electronics may designed such that the profile is thinenough, e.g., to fit into the back of a mobile phone enclosure. Asanother example, the resonator and electronics may designed such thatthe profile is thin enough, e.g., to be integrated into a sleeve orattachment for the mobile device, as well as a charging pad on which torest the mobile device. The sleeve or attachment may be fitted onto themobile device via a port of the mobile device. The energy captured bythe device resonator(s) and electronics may be used to charge thebattery of the mobile device directly (e.g., by a wired connection orvia a charging port of the mobile device). In some implementations, thesleeve or attachment for the mobile device may include one or moreshields made of, e.g., copper, magnetic material, aluminum, and thelike. In some implementations, a shield may be used to reduce magneticfield losses in the environment of the sleeve, reduce magnetic fieldlosses in the mobile device, and/or used as a guide for the magneticfield. The sleeve may, in some implementations, be designed such that itdoes not block ports, speakers, lights, cameras, and the like of themobile device. More in-depth descriptions and examples of shielding forwireless energy transfer may be found in one or more of the above-notedcommonly owned patent applications.

In some implementations, and referring at least to FIG. 2A, an exampledevice resonator coil 112 a is shown. As noted above, the resonator coilmay be integrated in, e.g., a mobile electronic device, a sleeve, orcase for a mobile electronic device, such as a mobile phone, asmartphone, a tablet, and the like. In some implementations, resonatorcoil 112 a may be optimized for the mobile electronic device toefficiently receive, e.g., at least 3 W of power, at least 5 W of power,or greater, and the efficiency of power transfer may be, e.g., greaterthan 30%, greater than 50%, greater than 70%, or more. FIG. 2B shows anexample implementation of a source resonator coil 112 b that may beintegrated into a pad, surface, tabletop, and like.

In some implementations, and referring at least to FIG. 3, anotherexample device resonator coil 112 c is shown. As noted above, theresonator coil may be integrated into a mobile electronic device, suchas a Bluetooth headset, a sensor, a wearable, and the like. In someimplementations, resonator coil 112 c may be optimized for an electronicdevice to efficiently receive, e.g., at least 0.5 W of power, at least 1W of power, or greater, and the efficiency of power transfer may be,e.g., greater than 10%, greater than 20%, greater than 30%, or more.More in-depth descriptions and examples of power transfer optimizationfor wireless energy transfer may be found in one or more of theabove-noted commonly owned patent applications.

As noted above, the wireless energy exchange between the sourceresonator and the device resonator may be optimized when the resonatorsare tuned to substantially the same frequency and when the losses in thesystem are minimal. As a non-limiting example, devices, such as a smartphone, may be powered directly, using the wirelessly supplied power orenergy, or the devices may be coupled to an energy storage unit such asa battery, a super-capacitor, an ultra-capacitor, or the like (or otherkind of power drain), where the energy storage unit may be charged orre-charged wirelessly, and/or where the wireless power transfermechanism may be supplementary to the main power source of the device.

However, while known resonator designs may be optimized while the sourceis at a distance from the device, these resonators may be less optimalin closer proximity. For instance, the source resonator may detune thedevice resonator as each resonator moves closer in proximity to oneanother. More specifically, for a wireless energy source having magneticmaterial, the inductance of the device resonator may be shifted as thedevice approaches the source, which may decrease efficiency. Whilemagnetic material may be used to reduce losses in the magnetic field dueto lossy materials in the environment or the electronics to which thesource resonator is coupled, an inductance shift in the device resonatormay still result in a greater-than-expected or lower-than-expectedoutput voltage. For instance, in the example scenario ofgreater-than-expected output voltage, the device resonator may sustaindamage to its electronics and/or to the load (such as a smart phone). Inthe example scenario of lower-than-expected output voltage, the deviceresonator may not be able to capture enough power for efficientoperation.

Wireless Energy Transfer System with Multiple Pieces of MagneticMaterial:

In some implementations, a source for wirelessly transferring energy mayinclude a plurality of layers. For instance, one of the layers mayinclude a conductive material (e.g., copper), which may be coupled to apower source. Another layer may include a magnetic material, and yetanother layer may include a resonator that is configured to exchangewireless energy with another resonator when each resonator is in closeenough proximity to one another. It will be appreciated that otherlayers may be included as well. As noted above, while magnetic materialmay be used to reduce losses in the magnetic field due to, e.g., lossymaterials in the environment or the electronics to which the sourceresonator is coupled, an inductance shift in the device resonator maystill result in a greater-than-expected or lower-than-expected outputvoltage. For instance, the inductance of the device resonator may beincreased in response to nearby magnetic material (e.g., such as whenthe device approaches the source to wirelessly charge). In someimplementations, to counter this increase, parts of the magneticmaterial used in the source may be removed or arranged. For example, asdiscussed above and referring also at least to FIGS. 4-5, a sourceresonator coil 406 with a center hole 410 in magnetic material 408 of anexample source (e.g., source 402) may cause the inductance of a deviceresonator to return to approximately its original value. Put anotherway, the “original value” of the device inductance may be broadlydescribed as the self-inductance of the device resonator in free space.In some implementations, and referring at least to FIG. 5, when anexample device (e.g., device 404) is offset relative to source 402, theinductance may still shift, which may be caused by, e.g., device 404being directly over magnetic material 408. For instance, assume forexample purposes only that for a 20 mm by 40 mm positional translationrelative to the center of source resonator 406, the inductance may stillvary, e.g., about 17%. As another example, for a 10 mm by 20 mmpositional translation relative to the center of source resonator 406,the inductance may still vary, e.g., about 5.6%.

In some implementations, the size, shape, geometric position, orcombination thereof of a plurality of pieces of the magnetic material inthe source may reduce inductance shifting in the device resonator whenproximate to the device resonator. For instance, and referring at leastto FIGS. 6-7, to avoid shifting the inductance, the magnetic materialmay be arranged in a plurality of horizontal bars 608 proximate tosource resonator coil 602. For instance, for an example 20 mm by 40 mmpositional translation of device resonator coil 604 relative to thecenter of source resonator coil 602, the inductance may vary about 15%.For an example 10 mm by 20 mm positional translation relative to thecenter of source resonator coil 602, the inductance may vary about 4.3%.

As another example, and referring at least to FIG. 8, in someimplementations, to avoid shifting the inductance, the magnetic materialmay be shaped and arranged in vertical bars 610 relative to sourceresonator coil 606. For instance, for a 20 mm by 40 mm positionaltranslation of device resonator coil 604 relative to the center ofsource resonator coil 606, the inductance may vary about 17%. For anexample 10 mm by 20 mm positional translation relative to the center ofsource resonator coil 606, the inductance may vary about 7.2%.

As yet another example, and referring at least to FIGS. 9-10, in someimplementations, to avoid shifting the inductance, the magnetic materialmay be arranged in a checkerboard pattern relative to the sourceresonator coil 902. For instance, the checkerboard pattern of magneticmaterial may be coarser, such as shown in example FIG. 9, or more fine,such as shown in example FIG. 10. In the example shown in FIG. 9 withthe coarse configuration of magnetic material 904, for an example 20 mmby 40 mm positional translation relative to the center of sourceresonator coil 902, the inductance may vary about 11%. For an example 10mm by 20 mm positional translation relative to the center of sourceresonator coil 902, the inductance may vary about 2.2%. In the exampleshown in FIG. 10 with the fine configuration of magnetic material 906,for an example 20 mm by 40 mm positional translation relative to thecenter of source resonator coil 902, the inductance may vary about 12%.For an example 10 mm by 20 mm positional translation relative to thecenter of source resonator coil 902, the inductance may vary about 1.4%.

As such, by using different shapes, sizes, and geometric patterns ofmagnetic materials for the source, the amount of inductance shifting forthe device resonator may be reduced. It will be appreciated thatdifferent shapes, sizes, geometric patterns and combinations thereof ofmagnetic material may be used without departing from the scope of thedisclosure. For example, at least a first portion of the plurality ofpieces of magnetic material may be a first shape (e.g., square), and atleast a second portion of the plurality of pieces of the magneticmaterial may be a second shape (e.g., rectangular). As another example,at least a first portion of the plurality of pieces of magnetic materialmay be a first size (e.g., 10 mm by 20 mm), and at least a secondportion of the plurality of pieces of the magnetic material may be asecond size (e.g., 20 mm by 40 mm). As yet another example, at least afirst portion of the plurality of pieces of magnetic material may be afirst pattern (e.g., checkered pattern), and at least a second portionof the plurality of pieces of the magnetic material may be a secondpattern (e.g., horizontal bars). As such, the description of particularsizes, shapes, and geometric patterns of magnetic material should betaken as example only and not to otherwise limit the scope of thedisclosure. As will be discussed in greater detail below, similarvariations in shapes, sizes, geometric patterns and combinations thereofof conductive material may be used, as well as mixing variations inshapes, sizes, geometric patterns and combinations thereof of conductivematerial and magnetic material may be used.

Wireless Energy Transfer System with Multiple Pieces of Conductivematerial:

As noted above, while magnetic material may be used to reduce losses inthe magnetic field due to lossy materials in the environment or theelectronics to which the source resonator may be coupled, an inductanceshift in the device resonator may still result in agreater-than-expected or lower-than-expected output voltage. In someimplementations, to avoid shifting the inductance of the deviceresonator, portions of the magnetic material and/or the source resonatorcoil of the source may be covered by conductive material.

As discussed above and referring also at least to FIG. 11A, an examplesource 1104 and device 1102 (not to scale) are shown. In the example,device 1102 may include a device resonator coil 1110 and a load (e.g.,represented as part of a mobile electronic device 1106). In someimplementations, a wireless energy transfer system may include a firstlayer of conductive material (e.g., conductive material 1114), whereinconductive material 1114 may be configured to cover some or all of thesurface of a power supply 1112. In some implementations, the first layerof conductive material 1114 may be copper. However, it will beappreciated that other examples of conductive material, such asaluminum, may also be used without departing from the scope of thedisclosure. In some implementations, the power supply may be a battery.However, it will be appreciated that other example power supplies may beused without departing from the scope of the disclosure.

In some implementations, a second layer of magnetic material (e.g.,magnetic material 1116) may be positioned proximate to (e.g., between)the first layer of conductive material and a third layer. In someimplementations, magnetic material 1116 may include ferrite. It will beappreciated that other magnetic materials may be used without departingfrom the scope of the disclosure. As discussed above, magnetic material1116 may be used to shield device resonator coil 1110 from mobileelectronic device 1106. In some implementations, magnetic material 1116may have a thickness less than 1 mm. In some implementations, magneticmaterial 1116 may have a thickness less than 0.5 mm. However, it will beappreciated that magnetic material 1116 may have various otherthicknesses depending on the desired characteristics of source 1104. Insome implementations, the thickness of the magnetic material may dependon the expected power level of transfer. Magnetic materials may saturatewhen exposed to higher magnetic fields at higher power levels. Thus,thicker magnetic materials may have higher saturation points. Forexample, for a source transferring approximately 10 W of power, 0.3 mmof magnetic material may be sufficient. In some implementations, thethickness of magnetic material may additionally range from, e.g., 0.3 to0.7 mm, 1 mm+, etc.

In some implementations, the third layer may be positioned proximate to(e.g., between) the second layer and a fourth layer, where the thirdlayer may include a plurality of pieces of conductive material (e.g.,pieces of conductive material 1118). As will be discussed in greaterdetail below, in some implementations, the pieces of conductive material1118 placed between source resonator coil 1120 and magnetic material1116 may have various shapes, sizes, and patterned positions (similar tothe above discussion of the pieces of magnetic material, as well asshown at least in FIGS. 6-10).

In some implementations, the fourth layer may be positioned proximate tothe third layer, wherein the fourth layer may include a first resonatorcoil (e.g., source resonator coil 1120), and wherein source resonatorcoil 1120 may be configured to transfer wireless energy with a secondresonator coil (e.g., device resonator coil 1110) when source resonatorcoil 1120 is proximate to device resonator coil 1110 (e.g., within thecharging area). For instance, as noted above, wireless energy transferbetween a source resonator (e.g., which may be coupled to a power supplysuch as AC mains, battery, solar panels, etc.) and a device resonator(e.g., integrated with mobile devices, enclosures, sleeves, cases,covers, chargers, etc.) which as is also noted above, may be used topower or charge the associated (mobile) electronic device.

In some implementations, source resonator coil 1120 may include coppertrace. For instance, source resonator coil 1120 may be designed within aprinted circuit board (PCB) using known techniques. It will beappreciated that, as appropriate, a PCB may encompass numerousvariations, such as a printed wiring board (PWB), a printed circuitassembly (PCA), printed circuit board assembly (PCBA), etc., orcombination thereof. As such, where appropriate, the term “printedcircuit board” or “PCB” used throughout may be interpreted as includingone or more of the above-noted variations. In some implementations, atleast one of the first, second, third, and fourth layers may be ondifferent planes of the PCB. For instance, in the example, assume thatat least a two layer (plane) PCB is used. In the example, the PCB maycontain source resonator coil 1120 on the second layer (e.g., secondplane) of the PCB, and the plurality of pieces of conductive material1118 may be on one or more different layers (e.g., first plane) of thePCB. In some implementations, various combinations of plane locationsmay be used without departing from the scope of the disclosure. Forinstance, a portion of the plurality of pieces of conducting material1118 may be located on one of the PCB planes, and a second portion ofthe plurality of pieces of conducting material 1118 may be located onanother of the PCB planes. In some implementations, two of the planesmay be the same plane. In some implementations, at least some of thelayers need not be part of the PCB. For instance, in someimplementations, conducting material 1114 may be a separate piece ofmaterial coupled to the top (or bottom) of the PCB. In someimplementations, only the two layers of the conductive material may bewithin the PCB, where the remaining layers may be outside the PCB. Assuch, the description of any number of layers being within a PCB shouldbe taken as an example only and not to limit the scope of thedisclosure.

In some implementations, the traces of source resonator coil 1120 may beincreased to increase its quality factor. For example, there may be agreater number of loops, greater amount of conductive material used tocreate the traces, and the like. More in-depth descriptions and examplesof resonator quality factor (i.e., Q-factor) for wireless energytransfer may be found in one or more of the above-noted commonly ownedpatent applications. In response, the pieces of conductive materialbelow source resonator coil 1120 may be decreased to compensate for theincreased amount of conductive material that device resonator 1110 may“see” or be affected by.

It will be appreciated that the order of the above-noted source layersmay be configured in a different order. For instance, referring at leastto FIG. 11B, source 1104 may have a first layer consisting of conductivematerial 1114, a second layer consisting of magnetic material 1116, athird layer consisting of one or more source resonator coils 1120, and afourth layer consisting of the plurality of pieces of conductivematerial 1118. In other words, in some implementations, the fourth layerconsisting of the plurality of pieces of conductive material 1118 may bethe outer layer that faces device 1102. As such, the described order ofthe “layers” should be taken as example only and not to otherwise limitthe scope of the disclosure. Similarly, the use of the terms “firstlayer”, “second layer”, etc. need not denote a particular order oflayers.

In some implementations, the first layer may be configured to be coupledto a surface of a mobile battery unit 1112. For instance, as notedabove, the above example configurations may perform satisfactorily toexchange wireless energy at a size small enough to be integrated as partof a mobile battery unit without necessarily changing the footprint ofthe mobile battery unit itself. In some implementations, the“connection” to mobile battery unit 1112 may be a physical mechanicalconnection, as opposed to a direct electrical connection (or viceversa). In the example, the resonator may include, e.g., ferrite andmetal shielding to prevent magnetic field interaction with mobilebattery unit 1112.

In some implementations, as will be discussed in greater detail below,source 1104 may include a plurality of source resonators. For instance,in some implementations, two or more source resonators may be used sideby side (e.g., horizontally or in the same plane as one another) withtheir respective horizontal axis aligned (or not aligned), as well asvertically (e.g., above/below) each other in different planes with theirrespective vertical axis aligned (or not aligned) to increase couplingbetween device resonator 1110 and at least one of the source resonators.In some implementations, the two or more source resonators may beconnected in series and/or in parallel. As such, the description of asingle (e.g., source) resonator should be taken as example only, and maybe interpreted as being more than one source resonator.

In some implementations, and referring at least to FIG. 12A, a sourceresonator coil 1202 may be symmetric about axis 1204. In someimplementations, source resonator coil 1202 may have a one or more loops(e.g., three or more loops, as shown in FIG. 12A) or four or more loops(as shown in FIG. 12C). It will be appreciated that any number of loopsmay be used according to the desired characteristics of source resonatorcoil 1202. For example, source resonator coil 1202 may be optimized fortransferring power to a wireless device resonator approximately 3 mm indistance away from the surface of source resonator coil 1202 (in theZ-direction or out of the page). In some implementations, the sourceresonator coil 1202 may be optimized for the size of the deviceresonator coil and/or for different distances to the device resonatorcoil. For example the distance may be 3 mm, 5 mm, 10 mm, or greater.

In some implementations, as discussed above and also referring at leastto FIGS. 12A-12H, the pieces of conductive material 1118 placed betweensource resonator coil 1120 and magnetic material 1116 may have variousshapes, sizes, and patterned (or non-patterned) positions (similar tothe above discussion of the pieces of magnetic material at least inFIGS. 6-10). In some implementations, at least one of a size, a shape,and a geometric position of the plurality of pieces of conductivematerial 1118 may reduce inductance shifting in the device resonatorcoil 1110 when source resonator coil 1120 is proximate to deviceresonator coil 1110. For instance, the pieces of conductive material1118 may be larger in size and placed closer to one another in thecenter of source resonator coil 1120 where there may be greater exposureto magnetic material, as seen by device resonator coil 1110. Forexample, FIG. 12B shows an example implementation with a plurality ofconductive material pieces 1118 that may be placed under sourceresonator coil 1202 (e.g., aligning axis 1204 from FIG. 12A with axis1204 from FIG. 12B) to decrease the variation in device resonator coil1110 inductance. In the example, various shapes, sizes, and geometricpatterns of the conductive material pieces 1118 are shown. For example,the shape may be a rectangle. As yet another example, the shape may be asquare. As yet another example, at least a first portion of theplurality of pieces of the conductive material 1118 may be a firstshape, and wherein at least a second portion of the plurality of piecesof the conductive material 1118 may be a second shape. As yet anotherexample, at least a portion of the plurality of pieces of the conductivematerial 1118 may be horizontal relative to a center of the firstresonator coil. As yet another example, at least a portion of theplurality of pieces of the conductive material 1118 may be verticalrelative to a center of the first resonator coil. As yet anotherexample, at least a portion of the plurality of pieces of the conductivematerial 1118 may be arranged in a checkered pattern relative to thefirst resonator coil. As can be seen from FIG. 12B, the pieces ofconductive material 1118 may be more dense and/or of greater sizetowards the center of source resonator coil 1202. In someimplementations, as noted above, the plurality of pieces of conductivematerial 1118 may be copper (or other conductive material).

As another example, and referring at least to FIGS. 12C-12D, sourceresonator coil 1206 may have four turns of conductive trace and beoptimized for transferring power to a wireless device resonatorapproximately 3 mm or greater in distance away from the surface ofsource resonator coil 1206 (e.g., in the Z-direction or out of thepage). Similar to FIG. 12B, FIG. 12D shows an example implementation ofconductive material pieces 1118 placed under source resonator coil 1206(e.g., aligning axis 1208 from FIG. 12C with axis 1208 from FIG. 12D) todecrease the variation in the device resonator coil inductance. In theexample implementation, the pieces of conductive material may be moredense and/or of greater size towards the center of source resonator coil1206.

As another example, and referring at least to FIGS. 12E-12F, sourceresonator coil 1202 (also shown in FIG. 12A) may be optimized fortransferring power to a wireless device resonator approximately 3 mm orgreater in distance away from the surface of source resonator coil 1202(e.g., in the Z-direction or out of the page). Similar to FIG. 12B, FIG.12F shows an example implementation of conductive material pieces 1118placed under source resonator coil 1202 (e.g., aligning axis 1204 fromFIG. 12E with axis 1204 from FIG. 12F) to decrease the variation in thedevice resonator coil inductance. In the example, the pieces ofconductive material 1118 may be slightly more uniform in shape, size,and pattern in the center of source resonator coil 1202 as compared toFIG. 12B.

As another example, and referring at least to FIGS. 12G-12H, sourceresonator coil 1206 (also shown in FIG. 12C) may be optimized fortransferring power to a wireless device resonator approximately 3 mm orgreater in distance away from the surface of source resonator 1206(e.g., in the Z-direction or out of the page). Similar to FIG. 12B, FIG.12H shows an example implementation of conductive material pieces 1118placed under source resonator coil 1206 (e.g., aligning axis 1208 fromFIG. 12G with axis 1208 from FIG. 12H) to decrease the variation in thedevice resonator coil inductance. In the example, the pieces ofconductive material 1118 may be slightly more uniform in shape, size,and pattern in the center of source resonator coil 1202 as compared toFIG. 12B.

It will be appreciated that other source and resonator designs may beused according to desired characteristics without departing from thescope of the disclosure. For example, and referring at least to FIG. 13,an example resonator coil 1302 may be optimized for transferring powerto a wireless device resonator approximately up to and including 46 mmin distance away from the surface of source resonator coil 1302 (e.g.,in the Z-direction or out of the page). In the example, the resonatorcoil 1302 may be approximately 142 mm by 192 mm. Further in the example,source resonator coil 1302 may be able transfer equal to or greater than10 W of power, greater than 15 W of power, greater than 30 W, or more.

In some implementations, as noted above, source 1104 may include aplurality of source resonators. For instance, and referring at least toFIG. 14A, an example two-layered resonator coil for a wireless energysource is shown. That is, layer 1404 may include one source resonatorcoil, and layer 1404 may include another source resonator coil. As such,the description of a single source resonator coil should be taken asexample only. In the example, the resonator coil may be optimized fortransferring power to a wireless device resonator at approximately,e.g., 6 mm (±1 mm) in distance away from the surface of the sourceresonator (e.g., in the Z-direction or out of the page). For instance,the two layers 1402 and 1404 of the resonator coil may be printed on twolayers of a PCB, where axis 1406 may align with axis 1408. The examplesource resonator coils may be able to transfer greater than 30 W ofpower. In some implementations, it may be beneficial to have two or morelayers of resonator coils to produce a magnetic field with minimumvariation in strength in one or more directional components. Forexample, a two-layer resonator coil may minimize variation in thestrength of the vertical component of the magnetic field. Themulti-layer nature of the resonator coil may enable greater movement inboth the X and Y offsets of the device resonator by creating asufficiently large active area. In some implementations, the active areamay be defined as the area over which the variation in the magneticfield is minimized. In some implementations, the two layers of the PCBcontaining each portion of the resonator coil may be printed on the PCBsuch that the layers are far apart enough to reduce or eliminate theparasitic capacitance that may occur between the traces on the twolayers. In some implementations, the layers containing each portion ofthe resonator coil may be at least 0.5 mm apart, at least 1 mm apart, atleast 2 mm apart, at least 4 mm apart, or greater. In someimplementations, the two layers of the PCB containing each portion ofthe resonator coil may be printed on a circuit board such that thelayers are far apart enough to reduce or eliminate the self-resonance ofthe resonator.

In some implementations, and referring at least to FIG. 14B, an exampleof a wireless power system is shown with two or more source resonators(e.g., 1410 and 1412) and a device resonator (e.g., 1414). In theexample, source resonators 1410 and 1412 may be switchably coupled to acontroller that may switch between source resonator 1410 and 1412respectively to transfer power at a height of Z₁ and/or Z₂. In someimplementations, and referring at least to FIG. 14C, an example of awireless power system is shown with two or more source resonators (e.g.,1410 and 1412) and two or more device resonators (e.g., 1414 and 1416).In some implementations, a controller may switch between two differentsource resonators 1410 and 1412, which may be configured for maximumfield uniformity and/or maximum resonator coil-to-coil efficiency. Forinstance, in one example, a controller may switch to one of the sourceresonators 1410, 1412 for maximum field uniformity at low Z-height Z1for the closer device resonator 1416. In another example, a controllermay switch to one of the other source resonators 1410, 1412 for maximumresonator coil-to-coil efficiency at a high Z-height Z2 for the furtherdevice resonator 1414. In some implementations, a controller may switchbetween two different source resonators 1410 and 1412 depending on thesize of the device resonator. For example, source resonators 1410 and1412 may be sized differently such that they can transfer powerefficiently to different sized device resonators. One of the sourceresonators may be smaller than the other and therefore may be able toaccommodate a small device resonator. The larger of the two sourceresonators may be turned off to conserve energy while the smaller sourceresonator may efficiently transfer energy to the small device resonator.

In some implementations, and referring at least to FIG. 14D, two sidesof an example source resonator (front side 1418 and back side 1420) areshown that may be formed on a PCB. In the example, the resonator may beable to transfer approximately, e.g., 16 W of power at a Z-height of 5mm. The resonator may include a distributed capacitance of, e.g., 220pF±2%. In the example, the resulting charging area at a Z-height of 5 mmmay be an area of, e.g., 160 mm by 150 mm.

In some implementations, and referring at least to FIG. 15, an exampleresonator coil 1502 for a wireless energy source is shown. In theexample, resonator coil 1502 may be optimized for transferring power toa wireless device resonator approximately between and including 26 mmand 46 mm in distance away from the surface of source resonator coil1502 (e.g., in the Z-direction or out of the page). In someimplementations, source resonator coil 1502 may be able to transfergreater than, e.g., 30 W of power. In some implementations, sourceresonator coil 1502 may be made of two resonator coils placed inparallel or series.

Wireless Energy Transfer System with Crossover Tracing:

In some implementations, a source resonator coil may be shaped (e.g.,via the windings of the resonator coil) to achieve a uniform chargingarea. For example, a uniform charging area may allow a device (via adevice resonator) to be charged at similar power levels throughout thecharging area (via a source resonator). In another example, a uniformcharging area may allow for similar low loss rates throughout thecharging area, thereby increasing efficiency. As will be discussed ingreater detail below, balancing currents throughout a coil (e.g., withparallel windings) may help achieve a uniform charging area and magneticfield, as well as creating a symmetric resonator coil.

As discussed above and referring also at least to FIGS. 16-20, awireless energy transfer system may include a first resonator coil. Forexample, a wireless energy transfer system may include a sourceresonator coil 1602, wherein source resonator coil 1602 may beconfigured to transfer wireless energy to a second/device resonator coil(e.g., of a device resonator) when source resonator coil 1602 isproximate to the device resonator coil. For instance, as noted above,wireless energy transfer to a source resonator (e.g., coupled to a powersupply such as AC mains, battery, solar panels, etc.) and a deviceresonator (e.g., integrated with mobile devices, enclosures, sleeves,cases, covers, chargers, etc.) may be used to power or charge theassociated mobile electronic device. In some implementations, similar tothe discussions of FIG. 11A, the source may include: a first layer ofconductive material, wherein the conductive material may be configuredto be coupled to a power source; a second layer of magnetic materialpositioned proximate to the first layer of conductive material and athird layer; the third layer positioned proximate to the second layerand a fourth layer, where the third layer may include a plurality ofpieces of conductive material; the fourth layer positioned proximate tothe third layer, wherein the fourth layer may include source resonatorcoil 1602. In some implementations, the third layer may include sourceresonator coil 1602; the fourth layer positioned proximate to the thirdlayer, wherein the fourth layer may include a plurality of pieces ofconductive material. In some implementations, the source may beconfigured similarly to the above-noted discussions of FIG. 11A or 11B.However, it will be appreciated that other combinations of sourceconfigurations may be used without departing from the scope of thedisclosure.

In some implementations, and referring at least to FIG. 16, a firstwinding of trace (e.g., winding 1604) may be included in sourceresonator coil 1602, wherein winding 1604 may include conductivematerial. A second winding of trace (winding 1606) may be included insource resonator coil 1602, wherein winding 1606 may include conductivematerial. In some implementations, the trace of at least one of thefirst winding and second winding may include copper coil for theconductive material.

In some implementations, windings 1604 and 1606 of the source resonatorcoil 1602 may be crossed, interleaved, or overlapped at a crossoverpoint. In some implementations, having a cross point in the coilwindings may help balance currents throughout the coil with parallelwindings. For example, a portion of the trace for winding 1604 may crossover a portion of the trace for winding 1606 at a crossover point (e.g.,crossover point 1608 a, 1608 b, 1608 c, 1608 d, 1608 e, 1608 f, 1608 g,and/or 1608 h). In some implementations, crossing the windings may helpto balance or approximately equate the currents (in each winding)relative to one another. Thus, in some implementations, the crossing ofthe coil windings may help achieve a symmetric resonator coil, which mayenable a more uniform magnetic field and charging area. In someimplementations, such as source resonator coil 1602, the windings of thecoil may be evenly spaced to help achieve the uniform charging area. Insome implementations, the crossover points may be beneficial incontaining the resonator coil in a plane. For example, many sourceenclosures restrict the resonator coil to be in a flat and thin pad-likemechanical enclosure such that it may have a low profile on a surface orbe mounted below a table.

For example, source resonator coil 1602 may be able to transferapproximately 16 W of power at a Z-height of, e.g., 46 mm. The chargingarea that may result from this implementation at a height of 46 mm maybe an area of around, e.g., 140 mm by 120 mm. In some implementations,two of the windings may be connected in parallel. For example, windings1604 and 1606 may be connected in parallel (e.g., winding 1604 may beconnected to 1610, and winding 1606 may be connected to 1612). In someimplementations, the crossover points may create a symmetrical resonatorcoil that creates a uniform magnetic field and balances impedances alongdifferent paths for traces driven in parallel. In some implementations,source resonator coil 1602 may include one or more capacitors connectedto windings at 1612 and 1610 to form a source resonator. Inimplementations, the source resonator coil, such as the source resonatorcoil shown in FIG. 16, may have uniform spaces between windings suchthat greater amount of conductive trace is used and therefore results ina resonator coil with a greater quality factor.

In some implementations, a second portion of the trace for winding 1604may cross over a second portion of the trace for winding 1606 at asymmetrical crossover point. For example, as can be seen at least fromFIG. 16, windings 1604 and 1606 may be configured to form multiplecrossover points (e.g., crossover point 1608 a, 1608 b, 1608 c, 1608 d,1608 e, 1608 f, 1608 g, and/or 1608 h). In the example, crossover point1608 d may be symmetrical to crossover point 1608 e. As another example,crossover point 1608 b may be symmetrical to crossover point 1608 f. Itwill be appreciated that non-symmetrical crossover points may be usedwithout departing from the scope of the disclosure.

In some implementations, the crossover point may occur in a middleportion of resonator coil 1602. For example, as can be seen at least atFIG. 16, the crossover points are located in the middle portion ofresonator coil 1602. By contrast, the crossover point may occur in anend portion of resonator coil 1602. For instance, and referring at leastto FIG. 12A, two crossover points are shown at the end portions ofresonator coil 1202 along axis 1204. That is, the two crossover pointsare shown at the elongated ends of resonator coil 1202. In someimplementations, the crossover points may be located at a combination ofmiddle and end portions of the resonator coil, as well as at any otherportions of the resonator. As such, the description of specificlocations of crossover points should be taken as example only and not tootherwise limit the scope of the disclosure.

In some implementations, and referring at least to FIG. 17, anotherexample resonator coil 1702 with crossover points is shown. For example,source resonator coil 1702 may be able to transfer approximately, e.g.,16 to 33 W of power at Z-height of, e.g., 6 mm. In the example, theresulting charging area at a Z-height of 6 mm may be an area of, e.g.,300 mm by 140 mm. In some implementations, resonator 1702 may includerounded and squared-off shapes to help achieve a uniform magneticfield/charging area for a given charging area. In the example, resonatorcoil 1702 includes two windings 1704 and 1706, connected in parallel(e.g., winding 1704 may be connected to 1708, and winding 1706 may beconnected to 1710). Further in the example, windings 1704 and 1706 maycreate crossover points (e.g., crossover points 1712 a, 1712 b, 1712 c,as well as other non-labeled crossover points shown in FIG. 17). In someimplementations, source resonator coil 1702 may include one or morecapacitors connected to windings at 1710 and 1708.

In some implementations, and referring at least to FIG. 18, anotherexample resonator coil 1802 with crossover points is shown. For example,source resonator coil 1802 may be able to transfer approximately, e.g.,33 W of power at Z-height of, e.g., 26 mm and 46 mm. In the example, theresulting charging area at a Z-height of 26 mm may be an area of, e.g.,220 mm by 150 mm. The resulting charging area at a Z-height of 46 mm maybe an area of, e.g., 210 mm by 140 mm. In some implementations,resonator coil 1802 may include two windings 1804 and 1806 connected inparallel (e.g., winding 1804 may be connected to 1808, and winding 1806may be connected to 1810). Further in the example, windings 1804 and1806 may create crossover points (e.g., crossover points 1812 a, 1812 b,1812 c, as well as other non-labeled crossover points shown in FIG. 18).In some implementations, source resonator coil 1802 may include one ormore capacitors connected to windings at 1810 and 1808.

It will be appreciated that other resonator coil designs may usecrossover points. For instance, example resonator coil designs that mayuse crossover points are similarly shown in the above-noted FIGS. 12A,12C, 12E, and 12G. Additional example resonator coil designs that mayuse crossover points are shown at FIGS. 19A and 19B, discussed below. Assuch, the description of any particular resonator coil design usingcrossover points should be taken as example only and not to otherwiselimit the scope of the disclosure.

In some implementations, the portion of the trace for the first windingmay cross over the portion of the trace for the second winding at thecrossover point with insulation between the portion of the trace for thefirst winding and the portion of the trace for the second winding. Forinstance, assume for example purposes only that the above-notedresonator coil 1602 from FIG. 16 is constructed on a single layer PCB.In the example, there may be insulation between winding 1604 and 1606 atthe crossover point (e.g., 1608 a).

In some implementations, the first resonator coil may be printed on aPCB, wherein the portion of the trace for the first winding may stop ona first side of the printed circuit board at the crossover point and maycontinue on a second side of the printed circuit board, wherein theportion of the trace for the second winding on the second side of theprinted circuit board may stop on the second side and may continue onthe first side after the crossover point. In some implementations, theportion of the trace for the first winding may cross over the portion ofthe trace for the second winding at the crossover point using differentlayers of a PCB. For instance, the portion of the trace for the firstwinding may stop on the first side of the portion of the trace for thesecond winding on a first layer of a printed circuit board beforereaching the crossover point, and may continue on the second side of theportion of the trace for the second winding on a second layer of theprinted circuit board after reaching the crossover point.

For instance, and referring at least to FIG. 20, an example resonatorcoil 2002 is shown. Assume for example purposes only that resonator coil2002 is constructed on a two layer PCB, with winding 2004 and 2006. Inthe example, winding 2004 may cross over winding 2006 by having thetrace of winding 2004 stop at point 2008 on the top layer of the PCB,and then continue at point 2010 on the bottom layer of the PCB (or viceversa).

It will be appreciated that other techniques to create crossover pointsmay be used without departing from the scope of the disclosure. As such,the example descriptions of crossover techniques should be taken asexample only and not to limit the scope of the disclosure.

Wireless Energy Transfer System with Current Sensing:

Known current sensing techniques that may be used for wireless energytransfer may, include, e.g., pickup loops around the trace or wire, HallEffect sensors, current sense transformers, current sense resistors,etc. These techniques may, e.g., have excessive loss and powerdissipation for the high current and high frequencies used in wirelessenergy transfer, may have frequency restrictions used in wireless energytransfer, may be susceptible to magnetic interference, may be expensive,and, assuming the techniques are incorporated in the device itself, mayadd to the size of the overall devices for which the current is beingmeasured.

Additionally, in measuring current in, e.g., a highly resonant wirelesspower transfer system, high frequencies and harmonics of the current, aswell as the magnetic field generated by the source resonator may presentchallenges in using the above-noted methods. In some implementations, aswill be discussed in greater detail below, a Rogowski coil may be usedas part of a current sensor for wireless power transfer systems.Rogowski coils may have, e.g., high repeatability, an ability to rejectinfluence from the magnetic field of the source resonator, and anability to determine root-mean-square (RMS) current from a voltage leveloutput. The measured coil (as well as the Rogowski coil) may be aconductor/conductive material or trace, such as copper, copper-cladsteel, Litz, and the like, and the measured coil may be driven with apower source (e.g., an AC source).

In some implementations, as will be shown in greater detail below, a(differential) current value of a conductor may be measured by routingthe conductor through the inner diameter D2 of the coil of conductivematerial. The conductor may be part of a resonator coil. For example, acurrent value of the resonator may be used, for example, for setting themagnetic field level in order to transfer power wirelessly, and as such,it may be useful to know its value. In some implementations, the currentmeasurement may be measured on a source resonator as a confirmation ofthe current levels and may be used as a feedback to control circuitry.For example, control circuitry may turn up or turn down power suppliedto the source resonator in response to a feedback signal from thecurrent sensor. In some implementations, the magnitude/amplitude valueand phase value relationships of the (e.g., AC) current measurements maybe used to measure impedance changes with the example disclosed currentsensing system(s). Other uses for the current measurement may be used aswell.

Rogowski coils as current sensors may be used for low frequencyapplications, such as 50-60 Hz for, e.g., power grid applications.Similarly, the above-noted methods of measuring current may fail whenapplied to signals greater than 1 MHz. They may also fail when placed ina magnetically noisy environment, such as those provided in (highlyresonant) wireless energy transfer systems. Thus, in someimplementations, the example current sensor may allow for, e.g.,measuring the high frequency current while rejecting magneticinterference on the sensor, may be easily repeatable from amanufacturing standpoint and have the capability of withstandingtolerances in manufacturing, and may include a parallel resonant filteror balanced filter to remove harmonic content and/or common-mode voltagein the measured signal. As will be discussed in greater detail below, insome implementations, the current sensor with the filter as a currentsensor may be produced on a printed circuit board (PCB), e.g., for awireless energy transfer system, and (1) may reject magnetic fieldeffects from the wireless energy transfer source resonator, (2) may beunaffected by DC offset in measured current, (3) may include the abilityto measure high frequency currents, (4) may not have the problem of coresaturation due to the lack of a magnetic material core, (5) may enableharmonics to be attenuated in the current signal due to the filter, (6)may not present a noticeable impedance shift or insertion loss on thesource resonator, (7) may be highly repeatable from a manufacturingstandpoint, (8) may be a small and low cost design since many of thecomponents, such as the Rogowski coil itself, may be made via traces inthe layers of the PCB, (9) may not result in significant change in thecapabilities of the sensor due to mechanical variation, and (10) mayenable an output that is a scaled voltage and easily measured.

As discussed above, and referring also at least to FIGS. 21-26, acurrent sensing system for wireless energy transfer may include aprinted circuit board (PCB), wherein the printed circuit board mayinclude at least a first layer, a second layer, and a third layer. Aloop of conductive material may be included, wherein the loop ofconductive material may include a diameter D3 on the second layer. Acoil of conductive material may be included, wherein the coil ofconductive material may have at least 2 turns, wherein the coil ofconductive material (e.g., a majority of the coil of conductivematerial) may occupy the first layer and the third layer with an outerdiameter D1 and an inner diameter D2, connected through each of thefirst, second, and third layers. The loop of conductive material may becoupled to the coil of conductive material.

For example, and referring at least to FIGS. 21-22, a coil of thecurrent sensor (e.g., current sensor coil 2102) may be designed tomaximize the number of turns in the area, as well as maximize of thearea of the coil itself. In the non-limiting example, current sensorcoil 2102 may have, e.g., 17 turns, with an outer diameter D1 of, e.g.,400 mm and an inner diameter D2 of, e.g., 200 mm. In someimplementations, a loop of conductive material may be included, whereinthe loop of conductive material may include a diameter D3 on the secondlayer. For example, current sensor coil 2102 may include a loop ofconductive material (e.g., one or more internal coils 2106 and 2108).The inner diameter D2 may be greater than the space available for themeasured conductor, for example, the diameter D4 of hole 2104. In someimplementations, the “footprint” or outer area may be kept small inorder to be a practical sized sensor on a small-sized PCB. In someimplementations, the sensor may be sized such that it may be created onthe same PCB as the conductor being measured (e.g., the source resonatorcoil). In some implementations, the loop of conductive material and thecoil of conductive material may form a Rogowski coil. For example, theRogowski coil may be formed by the loop of conductive material and thecoil of conductive material, where the loop may be connected to the coilat an end-point via (not shown in FIG. 22). In the example, the Rogowskicoil may occupy all layers of the PCB.

In some implementations, current sensor coil 2102 may be designed tomainly occupy the top 2204 and bottom 2210 layers of a PCB as well astwo inner layers 2206 and 2208, which may enable the closing of currentsensor coil 2102 in around itself. In some implementations, a coil ofconductive material may be included, such as coil windings 2110 and2112, which may have at least 2 turns. In some implementations, the coilof conductive material may have at least 15 turns. In someimplementations, a majority of coil windings 2110 and 2112 may occupythe first layer and the third layer with an outer diameter D1 and aninner diameter D2, connected through each of the first, second, andthird layers of the PCB. For example, the connection may occur in thevia that appears to be only connected to the coil on the bottom righthand side. The outer coil and the inner loop may be connected and maynot actually complete an entire loop as they may return instead to wherethey started. One or more internal portions of coils 2106 and 2108 maybe coupled to coil windings 2110 and 2112. In some implementations, theresult of coil windings 2110 and 2112, as well as the associated viasfor respective layers 2204, 2206, 2208, 2210 may effectively be toroidalin shape. Current sensor coil 2102 may be configured with at least oneof a straight return and a balanced winding (e.g., for the return loopof conductive material). For example, an example of the straight returnis shown in FIG. 21. As shown in example FIG. 21, the loop on the innerlayer does not wind or interleave with the coil on the outer two layers,therefore showing a straight return (e.g., no interleaving or winding).It returns straight back to the starting point where the connection maybe made. By contrast, a balanced winding may occur when forward andreverse paths wind around each other so that it becomes balanced, andwhere one path may not be shorter than the other. The balanced windingmay be interwoven with the original coil. The loop and the coil mayconnect at an end point via in such a way that a complete “connected”loop is not made. The coil may be configured with a balanced windingreturn loop of conductive material, where the conductive material mayoccupy the first and third layer in a way that avoids interference withthe coil of conductive material on the same layers. The balanced windingreturn loop may have outer diameter of D1 and an inner diameter of D2.In the example, the measurement may be proportional to the differentialof the current (instead of being directly proportional to the current).

In some implementations, top trace of coil winding 2110 may occupy firstlayer 2204, the second trace of internal coil 2106 may occupy secondlayer 2206, the third trace of internal coil 2108 may occupy third layer2208, and the bottom trace of coil winding 2112 may occupy fourth layer2210. In some implementations, various other layer PCBs may be usedwithout departing from the scope of the disclosure. For instance, afour-layer PCB may be more available for manufacture and thus chosenover a three-layer PCB. In some implementations, the fourth layer may bepositioned proximate to the second and third layers, wherein the fourthlayer may include an additional loop of conductive material (e.g., oneor more of the internal coils 2106 and 2108) coupled to at least one ofthe one or more internal coils 2106 and 2108 and the coil of conductivematerial (e.g., coil windings 2110 and 2112), wherein the additionalcircular loop of conductive material may have a diameter D3 on thefourth layer.

In some implementations, second and third traces of internal coils 2106and 2108 may occupy equal vertical space in a cross-section of afour-layer PCB or may be combined into a single trace in the case of athree-layer PCB. In some implementations, current sensor coil 2102 mayoccupy only three layers of the PCB, with top trace of coil winding 2110occupying a first layer, the second trace of internal coil 2106occupying a second layer, and the bottom trace of coil winding 2112occupying a third layer. The approximate area 2212 covered by sensorcoil 2102 may be given by taking the difference between the greaterdiameter D1 and the smaller diameter D2, and multiplying it by height2202. Height 2202 is shown by example as the thickness of the PCB, butthe dielectric material has been made transparent. Height 2202 may alsobe described as the distance between the top and bottom layer of currentsensor coil 2102 if current sensor coil 2102 does not occupy the entirePCB stack-up. On the other hand, if it does occupy the entire stack-up,then height 2202 may be equivalent to the thickness of the PCB.

In some implementations, current sensor coil 2102 may be able measurecurrents with frequencies within the approximate range of, e.g., 85 kHzto 20 MHz. In some implementations, e.g., for lower frequencies, currentsensor coil 2102 may be designed to have more turns and more area 2212to achieve a measurable output voltage. In some implementations, area2212 may be the loop area of the initial coil winding that wraps aroundthe internal straight return. The loop area may be dictated by, e.g.,the thickness of the PCB (e.g., height 2202) and the inner and outerdiameters (D1 and D2). In some implementations, the upper range offrequencies current sensor coil 2102 may measure may be determined bythe self-resonant frequency of the current sensor (as shown in FIG. 24and represented by L1 and C4 as modeling the (Rogowski) sensorself-resonant frequency). In some implementations, a current carrier ona PCB may be measured using this type of current sensor by, e.g.,increasing the number layers of the PCB. For example, in a six-layerPCB, the current carrier may occupy the first and last layer bytravelling vertically through all six-layers, while the current sensormay occupy the center four-layers of the six-layer PCB and wind aroundthe current carrier.

In some implementations, and referring at least to FIG. 23, exampleempirical measurements for the measured coil current output is shown. Inthe non-limiting example, waveform 2304 may be the coil current measuredand waveform 2302 may be the output voltage of current sensor coil 2102.In the example measurement, the RMS value of the coil current is 998.8mA and the RMS value of the output voltage of current sensor coil 2102is 302.2 mV. These values may be used (e.g., correlated for bestaccuracy or relative if not) in order to regulate the magnetic fieldlevel. Regulating the current based on receiving devices may also allowwider variations in coupling to have smaller ranges of voltage, sincethe voltage output levels may be proportional to the current levels (andhence magnetic field levels). This is one example. Other example usesmay be to ensure safe magnetic field levels, detect impedance changes orother changes that may change the coil current, etc. Using the coilcurrent phases and magnitudes of the multiple currents in its associatedmatching network may also be used to detect impedance at the coil.

In some implementations, a wire (which may be connected to a node in aresonant tank or to one of the nodes of a resonator coil) may passthrough a hole in the center of current sensor coil 2102 embedded in thePCB. In some implementations, a parallel resonant circuit may beincluded and may remove harmonic content. For example, current sensorcoil 2102 may be tuned with a resonant filter specifically targeted tominimize the harmonics in the measurement, and the output of the sensorcoil may be connected to measurement circuitry. In some implementations,a balanced filter circuit may be included and may remove harmoniccontent and/or common-mode voltage. In some implementations, themeasurement circuitry may filter and scale the signal in order to bemore easily read by a microprocessor, which may access the measurementof current sensor coil 2102.

For example, and referring at least to FIG. 24, an example schematic ofa current sensor, as well as the circuits that may be used to interfacewith the current sensor, is shown. In the example, the current sensor2402 may be modeled by an inductance L1 and a capacitance C4 that may beintrinsic to the sensor coil. R3, R4, L2 and C1 may be discrete circuitcomponents; L2 and C1 may be a resonant circuit that may have the sameresonant frequency of the measured current. In the example, currentsensor 2402 may be passive and the voltage source V1 may be a model ofthe magnetic field that the current sensor sits in. In someimplementations, a differential amplifier with a voltage output may beincluded. For instance, an integrating amplifier with differential inputand a single-ended voltage output may be included. For example, currentsensor 2402 may be connected to a differential amplifier 2404 that mayhave a single voltage output. Components R1 and R2 may be designed toload differential amplifier 2404. In some implementations, peak detectorcircuitry may be included and may include an operational amplifier totrack a peak of the voltage output and determine a measured(differential) current value of a conductor. For example, circuitry 2406may include an operational amplifier that may be used as a peakdetector, which may track the peak of the output voltage and maydetermine the measured coil current.

In some implementations, and referring at least to FIGS. 21 through 26,another example schematic of a current sensor, as well as the circuitsthat may be used to interface with the current sensor, are shown. In theexample, the size range may include, e.g., D1=0.375 to 0.8 inches,D2=0.19 to 0.4 inches, with D3 centered in the middle of D1 and D2, andwhere D4 may be dependent on desired wire gauge and may be irrelevant tooperation. In some implementations, the number of turns of the coil mayrange from approximately 16 to 36. However, it will be appreciated thatthis may be a small subset of what may be built. These variables may bedependent on desired frequency range, current range, etc.

The associated circuitry in FIG. 25 may be configured as a balanceddifferential amplifier, that may be configured with integration, may befollowed by a secondary gain stage (if necessary), and may be terminatedby an RF power measurement chip that may output a voltage relative tothe peak input voltage. As seen in the example, the two terminals on theleft (2502 and 2504) may come directly from a current sensor coil, andthe terminal on the right may terminate at the microprocessor.

In some implementations, and referring at least to FIGS. 24 and 26,example empirical results 2600 of a current sensor coil is shown. Themeasurements shown may be taken at the output of the peak detectorcircuitry (e.g., circuitry 2406) at different measured AC currentlevels.

In some implementations, a relationship may be established to predictthe output voltage of a given design of the current sensor coil. Forexample, the relationship may be given by:Vout=−C*u ₀ *u _(r) *N*A*(di/dt),

where C is a constant accounting for the PCB, u₀*u_(r) is thepermeability of the material between the current sensor coil and thecurrent carrier being measured, N is the turn density (e.g., turns permeter) of the current sensor coil, A is the cross-sectional area of thecurrent sensor coil (given by 2212 in FIG. 22), and (di/dt) is the rateof change of the current being measured. In some implementations, e.g.,where the current is a sine wave, the rate of change may be a sine wave.For other types of waves, such as square waves, integration electronicsmay be required.

In some implementations, the measured current may be found from theoutput voltage by first empirically measuring current levels of theconductor and corresponding output voltages of the current sensor, andcreating a reference table.

While the above disclosure may use examples of mobile electronicdevices, it will be appreciated that any type of electronic device maybe used without departing from the scope of the disclosure. As such, anyexamples of using mobile electronic devices should be taken as exampleonly and not to otherwise limit the scope of the disclosure.

The terminology used herein is for the purpose of describing particularimplementations only and is not intended to be limiting of thedisclosure. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps (notnecessarily in a particular order), operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps (not necessarily in a particular order),operations, elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements that may be in the claims below areintended to include any structure, material, or act for performing thefunction in combination with other claimed elements as specificallyclaimed. The description of the present disclosure has been presentedfor purposes of illustration and description, but is not intended to beexhaustive or limited to the disclosure in the form disclosed. Manymodifications, variations, substitutions, and any combinations thereofwill be apparent to those of ordinary skill in the art without departingfrom the scope and spirit of the disclosure. The implementation(s) werechosen and described in order to best explain the principles of thedisclosure and the practical application, and to enable others ofordinary skill in the art to understand the disclosure for variousimplementation(s) with various modifications and/or any combinations ofimplementation(s) as are suited to the particular use contemplated.

Having thus described the disclosure of the present application indetail and by reference to implementation(s) thereof, it will beapparent that modifications, variations, and any combinations ofimplementation(s) (including any modifications, variations,substitutions, and combinations thereof) are possible without departingfrom the scope of the disclosure defined in the appended claims.

What is claimed is:
 1. A wireless power source comprising: a printedcircuit board, wherein the printed circuit board includes at least afirst layer, a second layer, and a third layer; a current sensor createdon the printed circuit board, the current sensor comprising a loop ofconductive material, wherein the loop of conductive material includes adiameter D3 on the second layer, and a coil of conductive material,wherein the coil of conductive material has at least two turns, whereinthe coil of conductive material occupies the first layer and the thirdlayer with an outer diameter D1 and an inner diameter D2, connectedthrough each of the first, second, and third layers, such that the atleast two turns of the coil of conductive material wrap around the loopof conductive material, and wherein the loop of conductive material iscoupled to the coil of conductive material; a conductor routed throughthe inner diameter D2 of the coil of conductive material; and circuitrycoupled with the current sensor, the circuitry being configured to usethe current sensor to measure one or more values of current flowingthrough the conductor; wherein the circuitry comprises circuitryconfigured to remove harmonic content from a signal received from thecurrent sensor, a differential amplifier with a voltage output, and peakdetector circuitry including an operational amplifier to track a peak ofthe voltage output and determine a measured current value of theconductor.
 2. The wireless power source of claim 1, comprising aresonator coil comprising the conductor.
 3. The wireless power source ofclaim 1, wherein the printed circuit board comprises a fourth layerproximate to the second and third layers, wherein the current sensorcomprises an additional loop of conductive material occupying the fourthlayer, the additional loop of conductive material being coupled to atleast one of the loop of conductive material and the coil of conductivematerial, wherein the additional loop of conductive material has adiameter D3 on the fourth layer, and wherein the at least two turns ofthe coil of conductive material wrap around the additional loop ofconductive material.
 4. The wireless power source of claim 1, whereinthe coil of conductive material is configured with at least one of astraight return and a balanced winding.
 5. The wireless power source ofclaim 1, wherein the circuitry is configured to measure currents withfrequencies within a range of 85 kHz to 20 MHz using the current sensor.6. The wireless power source of claim 1, wherein the coil of conductivematerial has at least 15 turns.
 7. A wireless power source comprising: aprinted circuit board comprising three or more layers, including a firstlayer, a second layer, and a third layer; a Rogowski coil that occupieseach of the first layer, the second layer, and the third layer of theprinted circuit board, wherein the Rogowski coil comprises at least oneconductive trace on or within each of the first layer, the second layer,and the third layer of the printed circuit board; a source resonatorcoil that occupies at least one of the three or more layers of theprinted circuit board, wherein the source resonator coil comprises or iselectrically coupled with a conductor routed through the Rogowski coil;and circuitry coupled with the Rogowski coil, the circuitry beingconfigured to use the Rogowski coil to measure one or more valuescorresponding to current flowing through the conductor routed throughthe Rogowski coil.
 8. The wireless power source of claim 7, wherein thecircuitry comprises circuitry configured to remove harmonic content froma signal received from the Rogowski coil.
 9. The wireless power sourceof claim 8, wherein the circuitry comprises a differential amplifierwith a voltage output.
 10. The wireless power source of claim 9, whereinthe circuitry comprises peak detector circuitry including an operationalamplifler to track a peak of the voltage output and determine a measuredcurrent value of the conductor.
 11. The wireless power source of claim10, wherein the circuitry is configured to measure currents withfrequencies within a range of 85 kHz to 20 MHz using the Rogowski coil.12. The wireless power source of claim 7, wherein the Rogowski coilcomprises: multiple conductive traces on each of the first layer and thethird layer; and vias that pass through the second layer andelectrically couple the multiple conductive traces of the first layerwith the multiple conductive traces of the third layer; wherein themultiple conductive traces and the vias are, together, effectivelytoroidal in shape, and the effectively toroidal shape of the multipleconductive traces and the vias wrap around the at least one conductivetrace on or within the second layer.
 13. The wireless power source ofclaim 12, wherein the Rogowski coil comprises a straight returncomprising the at least one conductive trace on or within the secondlayer.
 14. The wireless power source of claim 12, wherein the printedcircuit board comprises a fourth layer between the second layer and thethird layer, the vias also pass through the fourth layer, the Rogowskicoil comprises at least one conductive trace on or within the fourthlayer, and the effectively toroidal shape of the multiple conductivetraces and the vias wrap around the at least one conductive trace on orwithin the fourth layer.
 15. The wireless power source of claim 12,wherein the Rogowski coil comprises a balanced winding.
 16. The wirelesspower source of claim 7, wherein the Rogowski coil has at least fifteenturns.
 17. A current sensor for wireless power transfer systems, thecurrent sensor comprising: a printed circuit board comprising a firstlayer, a second layer, a third layer, and a fourth layer; and a Rogowskicoil that occupies each of the first layer, the second layer, the thirdlayer, and the fourth layer of the printed circuit board; wherein theRogowski coil comprises multiple conductive traces on each of the firstlayer and the fourth layer of the printed circuit board, vias that passthrough the second layer and the third layer and electrically couple themultiple conductive traces of the first layer with the multipleconductive traces of the fourth layer, and at least one conductive traceon or within each of the second layer and the third layer of the printedcircuit board, wherein the multiple conductive traces and the vias are,together, effectively toroidal in shape, and the effectively toroidalshape of the multiple conductive traces and the vias wrap around boththe at least one conductive trace on or within the second layer and theat least one conductive trace on or within the third layer.
 18. Thecurrent sensor for wireless power transfer systems of claim 17, whereinthe printed circuit board comprises six layers, which include a centerfour layers being the first layer, the second layer, the third layer,and the fourth layer, and the current sensor comprises: a currentcarrier that occupies all of the six layers and passes verticallythrough the center four layers of the six layers of the printed circuitboard; wherein the Rogowski coil occupies the center four layers of thesix layers of the printed circuit board, and the Rogowski coil windsaround the current carrier.
 19. The current sensor for wireless powertransfer systems of claim 17, wherein the conductive traces on or withinthe first layer, the second layer, the third layer, and the fourth layerof the printed circuit board are copper traces.
 20. The current sensorfor wireless power transfer systems of claim 17, wherein the Rogowskicoil has at least fifteen turns.
 21. The current sensor for wirelesspower transfer systems of claim 20, wherein the Rogowski coil hasseventeen turns, an inner diameter of 200 millimeters, and an outerdiameter of 400 millimeters.